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Background: Idelalisib (IDELA) is a first-in-class, selective, oral inhibitor of PI3Kδ that reduces proliferation, enhances apoptosis, and inhibits homing and retention of malignant B cells in lymphoid tissues. Phase 1 trials demonstrated that IDELA is highly active as a single agent or in combination with rituximab (R) in heavily pretreated patients (pts) with CLL. Pts in these trials experienced reductions in disease-associated chemokines, improvement of organomegaly and cytopenias, profound reductions in lymphadenopathy, and durable clinical benefit with an acceptable safety profile (Brown 2013; Barrientos 2013). Patients with early progression and significant co-morbidities have limited treatment options; single-agent rituximab is an option in these pts (NCCN 2013; Zelenetz 2013).

Methods: This Phase 3 study evaluated the efficacy and safety of IDELA + R vs placebo + R in pts with previously treated CLL. Eligibility criteria included the need for treatment per IWCLL guidelines, measurable lymphadenopathy, and CLL progression <24 mos since the completion of last therapy. Pts were considered unfit to receive cytotoxic therapy because of comorbidities (defined as a Cumulative Illness Rating Score [CIRS] > 6), renal dysfunction, or cytopenias due to poor marrow reserve. All pts received R at 375 mg/m2 [1st dose] and then 500 mg/m2q2 wks x 4, followed by q4 wks x 3 [8 doses total]) and were randomized to Arm A (n=110; IDELA 150 mg BID continuously) or Arm B (n=110; placebo BID continuously). Primary endpoint was progression-free survival (PFS). Response and progression in both arms were assessed by an independent review committee using standard criteria (Hallek 2008; Cheson 2012). Results were reviewed by an external Data Monitoring Committee (DMC).